disc2prob - direction from the roof of a building 30.0 m...

Physics 1A Discussion January 20, 2012 1. 1D Rocket A rocket’s engines have failed, and it is in free fall from a height of 5000 m from rest. The pilot can reignite the engines, at which point the rocket’s acceleration is 30 m/s 2 upward. You can neglect air resistance. (a) What is the minimum height the pilot can reignite the engines without crash-ing? (b) What is the total elapsed time from when the rocket started its free fall (from rest) to when it reaches 5000 m again? 2. Crashing Planes A plane has just taken oﬀ and is ﬂying with a velocity of v0 = 90 m/s at an angle of θ = 23 .0 ◦ above horizontal. When the plane is at a height of h = 114 m, its engines fail. You can neglect air resistance. (a) How much farther does the plane go before crashing into the ground? (b) Calculate the magnitude of the velocity (in variable form) of the plane just before it crashes. Note that this is independent of the angle θ . 3. [YF 3.57] A toy rocket is launched with an initial velocity of 12.0 m/s in the horizontal

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Unformatted text preview: direction from the roof of a building 30.0 m tall. The rocket’s engine produces a horizontal acceleration of αt in the same direction as the initial velocity, where α = 1 . 60 m/s 3 . In the vertical direction, the acceleration is g downward. Air resistance can be neglected. What horizontal distance does the rocket travel before reaching the ground? 4. [YF 3.73] Two tanks are engaged in a training exercise on level ground. The ﬁrst tank ﬁres a paint-ﬁlled training round with a muzzle speed of 250 m/s at 10.0 ◦ above the horizontal while advancing toward the second tank with a speed of 15.0 m/s relative to the ground. The second tank is retreating at 35.0 m/s relative to the ground, but is hit by the shell. You can ignore air resistance and assume the shell hits at the same height above ground from which it was ﬁred. Find the distance between the tanks: (a) when the round was ﬁrst ﬁred, and (b) at the time of impact....
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